Process of hydrating lime and utilizing heat of hydration.



H. L. DOHERTY. PROCESS OF HYDRATING LIME AND UTILIZING HEAT 0FHYDRATION.

APPLICATION FILED APR. 20, 1911. RENEWED DEC. 24, 1912.

1,066,719. Patented July 8, 1913.

w'gtmwoeo UNITED STATES PATENT OFFICE.

HENRY L. DOHERTY, OF NEW YORK, N. Y.

PROCESS OF HYDRATING LIME'AND UTILIZING HEAT 0 HYDRATION.

Patented July 8, 1913.

Application filed April 20, 1911, Serial No. 622,357. Renewed December24, 1912. Serial No. 738,474.

To all whom it may concern:

Be it known that I, HENRY L. Donnn'rr, a citizen of the United States,and a resident of New York city, in the county of New York and Stateot'iNew York, have invented certain new and useful Improvements inProcesses of Hydrating Lime and Utilizing Heat of Hydration, of whichthe following is a specification.

This invention relates to a process of hydrating lime and utilizing heatof hydration, and in particular to such a process in which the heatdeveloped in the hydration of the lime is communicated to the air usedin supporting the combustion in the kiln.

The object of my invention is to reduce the amount of fuel that isrequired in the burning of the lime by recuperating the heat developedin the hydration of the lime, as well as the manufacture of lime hydratefrom limestone in what is substantially one operation. By my invention,I enter the limestone at the top of the kiln and withdraw the hydratedlime at the bottom.

In carrying out my invention, I introduce into the lime kiln, below thecooler of the same, two chambersa hydrating chamber and a separatingchamber. The lime after passing through the kiln enters the hydratingchamber where a current of air mixed with suflicient steam to hydratethe lime is passed through it. The air, heated by the heat developed bythe reaction in the hydrating chamber, is divided into two currents. Onecurrent. passes up through the kiln in contact with the hot lime in thecooler of the kiln, where it is further heated, and thence into thecombustion zone of the kiln where it is used to burn the fuel. The othercurrent of the air, which has been heated in the hydrator, is withdrawnby a suitable blower and forced togetherwith fresh air through anevaporating chamber where it is contacted with. water. The sensible heatof the air (which has been derived from the sensible heat of the limeand the heat liberated in the hydration) is, in part, given up to thewater which is evaporated, the steam so formed mixing with the air. Thesteam laden air current is conductedinto the hydrating chamber andpassed through the lime therein where the steam is taken up by the lime,as before.

In the accompanying drawings, in which Figure 1 is a sectional view andFig. 2 a detail view, I have shown a form of apparatus suitable forapplying my invention.

1 is the lime-kiln, which has the shaft 2. in which the lime is burned,the lower part 3 of 2 being used as a cooler for the hot lime.

4 indicates the doors closing the bottom of the cooler 3.

5 is the hydrating chamber, (3 the doors closing the bottom of the same.

7 is the dust separator, closed by the doors 7.

8 is the evaporating chamber, 9 the dust catcher for removing the finelydivided bydrate taken up in 6 from the separator air.

10 is the blower which maintains the circulation through the hydratingand evaporating chambers, 11 the blower maintaining the circulation ofair through the dust separator 7 and dust catcher S).

In operating my invention, I may use any type of kiln preferred, butprefer to use a kiln of the type figured in which producer gas isburned. The limestone is charged into the kiln in the usual way in largelumps through the charging doors 12. The gas producer 13, having beenbrought up to the proper operating condition in the manner well known tothose skilled in the art of produccr operation, the gas from theprmluccr passes through the connection 14 to the bustle-pipe 15, fromwhich it is distributed through the passages 16 to the shaft of thekiln. Here it is burned by heated air that has passed through thehydrator 5 and the cooler 3, as described below. The gas is burned incontact with the partially cal cincd lime, completing the calcination ofthe same, the combustion gases thence passing up through the uncalcinedstone, and the stone in various degrees of calcinatiou, yielding uptheir heat to the same, finally discharging from the kiln through thestack 17. Part of the combustion gases are withdrawn from the kilnthrough the pipe 18 and diverted to the producer by the blower '19,togetherwit h air drawn into the blower through the dampcr 20 on thesuction pipe 21. The proportion of combustion gas and air supplied tothe gas producer is so rcgulated that the absorption of heatfrom thefuel bed of the producer through the reduc- .ash of the fuel usedtherein.

(a). oo +e=2co,

a H2O+C=H2+OO,

will just about balance the heat developed by the reaction,

(a) C+O=CO,

of the oxygen of the air with the carbon of the fuel, in themannerdescribed in my Letters Patent No. 938,987, dated Nov. 2nd, 1909,so that the temperature in the fuel bed is kept below the fluXingtemperature of the Thea hot burned lime descends through the cooler ofthe kiln, where the heated air from the hydrator is passed through it,and thence is discharged into the hydrator The airsteam current entersthe bottom of the hydrator 5 through the pipe 32, and passes up throughthe lime in the same, yielding up its water vapor to the lime to formhydrate of lime. As the lumps of quicklime take up the water vapor theygradually fall to pieces, the flour-like hydrate being removed from theexterior of the lumps by the and mutual attrition which they exercise on1 each other as the mass is caused to pass downward through thehydrating chamber. The lime enters the hydrating chamber for the mostpart in large lumps. As these lumps pass downward through the hydratingchamber, they continually diminish in size;

but I purposely regulate the rate at which I Withdraw the material atthe bottom of the hydrator, so that the larger lumps are only partiallyhydrated, or slaked. I thus leave a sufficient proportion of largefragments in the mass to maintain voids to keep the latter in asufliciently open condition to permit of the ready passage of the draftcurrent. At intervals, I Withdraw from the bottom of the hydrator byopening the dis- "through the separator.

. ried into the dust separator 7, through the charging doors 6, aportion of the partially hydrated mass. This falls through the pneumaticseparator 7, through which an air current forced by the blower 11. The

mass of material charged into 7 from 5 con sisting of fine hydrate'andthe unhydrated fragments is intercepted by the uppermost grate 23 of thehydrator. By shaking the bars of 23, through the operation of the lever23 and the connections 23 to 23, the material is caused to graduallypass through 23 and falls on to the grate 24, and so on The fine flourlike hydrate is winnowed out of the mass by the air current enteringthrough 22 and is carpipe 27 where it is filtered out of the air currentby bags or in any other suitable manner, according to the type of dustcatcher used. The air, freed from its load of hydrate, again passes tothe suction side of blower 11 through the pipe 28, discharging from thesame through the pipe 22 to the separator 7 as before. The advantage inthus using the separator air in a closed circuit is that the hydrate isthus not exposed to the action of the CO of the air.

While the possible contamination of the hydrate due to using theuntreated atmospheric air is not serious, still, I find some advantagein this method of using the separator air in a closed circuit. Theunhydrated lumps and the particles too coarse to be capableof suspensionin the air current are withdrawn from the dust separator 7 through thechute 18 by opening the dischargedoors 7 and raised by the elevator 29to the chute 30, through which it passes, on opening the gate 31, backinto the hy drator 5. Mixing with fresh quicklime from the cooler 3 thisunhydrate'd material again passes through the hydrator where it iscompletely hydrated, the large lumps of the fresh charge of quicklimeproviding new material for keeping the charge open and permeable to theblast.

In starting operations, the water for the hydration is introduced in theform of steam into the air current passing through the pipes 32 and hood33, through the perforated pipe 34 which encircles theair pipe 32.

Steam is supplied to 34 through the pipe by opening valve 36. The steamis carried by the air current into the mass in the 'hydrator and istaken up by the lime to form hydrate. The reaction CaO+I-I O:C aO I-Iwhen the H. is supplied as steam, liberates about 969 B. T. U. (above 32Fah.) per pound of CaO reacting. While it is true that, at first, s01 esteam is condensed, the heat developed prevents any supersaturating ofthe lime with water. As the operation proceeds, the charge in 5gradually builds up in temperature, raising the temperature of the airleaving the top of the hydrator. When the blower 10 is first started thevalve 37 on the pipe 42 is closed and damper 41 opened. When the airdischarging from the hydrate-r into the cooler of the kiln has beensufficiently heated, the damper 41 is partially closed. and the valve3'? opened. Part of the hot air is now drawn off from the hydrator 5through the pipe 42 and forced through the evaporator 8. VVater isgradually turned on to the ans 38 by partially opening the valve 39 onthe wa ter supply pipe 40. The sensible heat of the air is communicatedto the water in the pans 38 both by direct contact between the water andair and by heat conducted through the pans themselves from the hot airpassing along their bottoms. The quantity of water admitted at thisstage is restricted to the quantity which can be evaporated by the heatof the air circulated through 8, without reducing the temperature of themixture below a temperature well above the boiling point. It isdesirable that the temperature of the air-steam mixture leaving theevaporator should be well above the boiling point in order to insurethat there will be no condensation of steam due to heat losses in thepipe 32 When the temperature of the portion of air drawn from thehydrator through the pipe 42 has reached a point such that its sensibleheat above the temperature at which the air-steam mixture is introducedinto the hydrator, is sufhcient to evaporate the proportion of waterrequired in the hydration, the valve 36 is closed and the valve 3.) setso that the proper proportion of water is injected into the heated aircurrent. As the temperature of the air leaving the hydrator rises, theproportion of air withdrawn through 42 is cut down. It is only necessarythat the volume of air withdrawn through the pipe 42 should besullicient to carry into the evaporator 8 the quantity of heat requiredto evaporate the water, and leave the temperature of the mixed air-steamcurrent leaving the evaporator above 212 Fah. As shown, the doors 4closing the bottom of the cooler and supporting the charge in the kiln,are preterably of a grated construction or in the formof hinged grids.The air from. the hydrator 3M1 thus pass t'reely up into the relativelyhot lime in the cooler 3. The natural tendency of the air current is topass directly into the cooler, and, in order to divert a portion of itto the evaporator, it is necessary that the suction exercised by theexhauster-blower 10 should be superior to the draft of the kiln.

It is to be noted that the heat which I withdraw from the hydrator 5 inthe air taken oft-through 42 to evaporate the water for the hydration,is not lost to the calcining operation, since the-latent heat ofevaporation of the water is again liberated in the hydrating chamberwhen the water combines with the lime. The only heat which is lost tothe calcination by my method of working is that due to condensation andradiation losses from the draft current passing through the system fromthe top to the bottom of the hydrator 5. The object in thus introducingthe water into the hydra tor 5 as steam, is that I thereby securefa moreuniform hydration and automatically insure the production of a perfectlydry hydrate.

Since the theoreticalv heat absorption in the dissociation of limestoneper pound of lime produced is about 1400 B. T. U., and the theoreticalheat development in the hydration of 1 lb. of limeis 485 B. T. U., it isseen, that the proportion of the heat of calcination which I return tothe calcining operation by utilizing the heat developed in the hydrationof the lime to heat the air used for supporting the combustion in thecalcining operation is about one-third of the theoretical requirement.

llaving described my invention, what I claim is:

l. The method of recuperating the heat of hydration olf lime in theburning of lime which comprises, continuously circulating air first incontact with hot lime, whereby said air is heated, second in contactwith water to evaporate the same, whereby the, said air is mixed withwater vapor, and third circulating the mixture of air and water vapor incontact with quicklime, to hydrate said quickliine and to heat said airby the heat developed in said hydrating reaction, the said heatcomprising the latent heat of evaporation of said water and the normalheat of hydration of said lime, and

diverting from said circulating air current atterit has been contactedwith and heated by said hydrating lime the portion of the same requiredfor sustaining the combustion of the fuel required for burning saidlime.

2. The method of utilizing the heat of hydration of lime whichconsists'in mixing water-vapor with air to be used in sustaining thecombustion of fuel, passing the wat:e1 '-vapor laden air in contact withquicklime whereby the water-vapor of said air is absorbed by saidquicklime to form hydrated lime and the said air heated, withdrawing aportion of said heated air and passing it in contact with water, wherebysaid water a u I is evaporated by the heat of said portion ot air,mixing the water-vapor laden air with another portion of air, andcontacting the said mixture with quicklime.

3. The method of utilizing the heat of hydration of lime in the burningof lime which comprises, continuously circulating a current of air firstin contact with hot lime, whereby said air is heated, second in contactwith water to evaporate the same, whereby the said air is mixed withwater vapor, and third circulating the mixture of air and water vapor incontact with quicklinie to hydrate said quicklime by said water vaporand to heat said air by the heat developed in the hydration of saidlime, said heat comprisin the chemically developed heat of the hydratingreaction and the latent heat of said water vapor, diverting from saidcirculating air current after the same has been heated the portion ofthe same required for sustaining the combustion of the fuel necessaryfor burning said lime, and adding to the residual hot air of thecirculating current before the same is contacted with water a weight ofair substantially equal to the Weight of the diverted air.

4. The process of utilizing the heat of 'a1r heated, contacting aportion of said heated air with water, whereby the said water isevaporated and the water-vapor formed mixed with said portion of air,adding fresh air to such mixture and passing the resulting mixture ofair and watervapor in contact with more quicklime whereby the saidquicklime is hydrated and the said air heated.

5. The process of recuperating heat in the burning of lime whichcomprises, continuously circulating a current of air first in contactwith heated lime, whereby said air is heated, second in contact withwater to evaporate the same, whereby the said air is mixed with watervapor, and third circulating the mixture of air'and water vapor incontact with quicklime to hydrate said,

quicklime by said water vapor and to heat said air by the heat developedin the hydration of said lime, said heat comprising the chemicallydeveloped heat of the hydrating reaction and the latent heat of saidWater I vapor, diverting from said circulating air current after thesame hasbeen heated, the portion of air required for sustaining thecombustion of the fuel necessary for burning said lime, passingsaiddiverted air first in contact with the freshly burned lime tofurther heat said air and then' into-the region in which said lime isbeing burned,

and adding to the residual hot air of the circulating current before thesame is contacted with water a weight of air substantially equal to theweight of the diverted air.

6. The process of utilizing the heat of hydration of lime which consistsin hydrating lime in a closed chamber by contacting the same with acurrent of air laden with watervapor, whereby the said lime is hydratedand the said air heated, continuously withdrawing from said heated aircurrent a volume of the same which will contain suflicient heat tovaporize the water required in the hydration of said lime, passing thesaid vol' ume of heated air in contact with water, whereby the saidwater is vaporized and the said vapor mixed with said air, passing thesaid air-water-vapor mixture through the lime in said closed chambertogether with the volume of air that is required to sustain thecombustion in the kiln in which said lime is burned, whereby a furtherportion of the lime. in said chamber is hydrated and the said'airheated, and passing the necessary proportion-ofsuch heated air into thelime-kiln in which said lime is burned to sustain the combustiontherein.

' 7 The process of utilizing the heat of hydration of lime whichconsists in burning the said lime in a kiln with preheated air, chargingthe said lime into a hydrating chamber, hydrating the said lime in said1 Chamber by continuously passing therethrough a current of air loadedwithv watervapor, whereby the said lime is hydrated and the said aircurrent heated, the said water-vapor being generated by continuouslydiverting a volume of such heated air containing sufficient heat togenerate the said water-vapor through a closed chamber in which it iscontacted with the proper proportion of water, whereby the said water isvaporized, passing the water-vapor-laden air together with the air forsustaining the combustion in said kiln through the lime in saidhydrating chamber, whereby a further portion of said lime is hydratedand said air heated, and passing the heated combustion air into saidkiln to sustain the combustion therein.

8. In the manufacture of hydrated lime, the process which comprises,passing air in contact with hydrated lime to heat said air, passing saidheated air in contact with water to evaporate water by heat developed inthe hydration of said lime and to form a mixture of air and water vapor,transmitting quicklime through a hydrating region,

lime is hydrated by water vapor formed by heat developed in thehydrating reaction;

9 In the manufacture of hydrated lime, the process which comprises,transmitting quicklime through a hydrating chamber. continuouslycirculating a gaseous medlum which is substantially non-reactive withquicklime in a closed circuit through said hydrating chamber and anevaporating chamber, said evaporating chamber containing water, wherebysald gaseous medium 1s caused to take up heat'developed in thehydrationof said quicklime to transfer said heat to the water in said evaporatingchamber to evaporate said water and to form an admixture of Water vaporwith said gaseous medium, and to transport the so-formed water vaporinto contact with said quicklime, whereby the said quicklime issubjected to hydration by water vapor diffused through a body of diluentgas.

Signed at New York city in the county of New York and State of New Yorkthis 19th day of April A. D. 1911.

HENRY L. DOI lERTY. Witnesses p FRANK L. BLACKBURN, THos. I. CARTER.

